In the past we have studied intestinal barrier function in developing rabbits (1,2). We have noted that newborn rabbits transport increased amounts of the common blood antigen, bovine serum albumin, from the intestinal lumen into the circulation than adult animals. We now propose to extend these studies and evaluate intestinal and hepatic defense mechanisms in immature animals using known hepatotoxins (proteases and endotoxin) which may normally be present in the intestine. Using substrate assays and a radioimmunoassay we will quantitate serum protease levels prior to and following gavage feeding trypsin and chymotrypsin. Breast- and bottle-fed animals will be gavage-fed these proteases for several weeks, thereafter serum from these animals will be tested for changes in alpha-fetoprotein levels. Liver tissue will also be evaluated histologically for evidence of inflammation. Mucosal and hepatic defense against gavaged proteases will be further evaluated in immature animals stressed by acute starvation, gastroenteritis and malnutrition. In additional studies, we will evaluate the uptake and clearance of E. coli endotoxin in developing rabbits. To determine if early nutrition affects defense mechanisms studies will be conducted in breast- and bottle-fed animals (2). The transport of E. coli endotoxin across the intestine of animals at different stages of development will be performed using an immunoradiometric assay to detect endotoxin in portal and systemic blood. To determine whether the liver of newborn animals is more sensitive to endotoxin, E. coli endotoxin will be gavage fed these animals and liver enzymes and architechture evaluated. Kupffer cell function will be examined in the animals by comparing endotoxin levels in portal and systemic blood. The clearance of intravenously injected colloid substances which have been shown to reflect Kupffer cell function will be compared in immature and mature animals. In addition, Kupffer cells will be isolated from the lives of developing rabbits and phagocytic and lysosomal enzyme release studied. Data obtained from evaluating mucosal and hepatic defense mechanisms early in life and determining whether the transport of hepatotoxic macromolecules (proteases, endotoxin) is associated with liver inflammation may enable us to better understand the pathogenesis of the "neonatal hepatitis syndrome".